1. Field of the Invention
This invention relates to dental compositions. In particular, this invention relates to dental compositions comprising degradable copolymers which are suitable for use as root canal sealants, root canal filling materials, implant materials, and in pulp capping.
2. Description of the Related Art
Endodontic therapy for a diseased or otherwise compromised tooth generally involves the dental practitioner accessing the root canal, debriding and disinfecting the root canal to clean and remove all of the soft tissue (the pulp) therein, and then enlarging the canal to remove irregularities or rough surfaces within the canal. A pre-formed xe2x80x9cconexe2x80x9d or xe2x80x9cpointxe2x80x9d is then inserted into the canal, and the cone is laterally or vertically condensed into the canal so that the point of the cone terminates at the apex of the canal. A commonly used cone material is gutta percha, which is a thermoplastic rubber. Because of the many irregularities which remain in the surface and shape of the canal even after treatment, it is difficult to achieve a satisfactory seal between the apex of the root canal and the cone without use of a root canal filler or sealant. Numerous sealants have been described, for example swellable hydrophilic acrylates and methacrylates such as 2-hydroxyethyl methacrylate (HEMA), as disclosed in U.S. Pat. No. 3,925,895 to Kliment et al. The monomers are mixed with polymerization initiator immediately prior to use and delivered to the root where polymerization occurs in situ. U.S. Pat. No. 4,986,754 discloses an injectable endodontic filling material comprising a mixture of balata or gutta percha with a liquid plasticizer. U.S. Pat. No. 4,449,938 discloses use of a two-component, room temperature setting organopolysiloxane compositions used for dental impression materials.
Despite these advances, the most commonly used root canal sealants remain compositions comprising a mixture of zinc oxide with eugenol (ZOE), and mixtures comprising calcium hydroxide. ZOE in particular is irritating to some patients, and has low adhesion to the walls of the root canal. Root canal sealants should be non-toxic, non-irritating, radiopaque, and have no or minimal shrinkage. They should also set within a reasonable period of time. They must be biologically compatible with tooth structure, and are preferably inert to moisture and to the pH conditions found in the mouth. Ideal preparations have low viscosity to facilitate insertion into the root canal, and even more preferably, are thixotropic. In the case of overflow of root canal sealant from the apex into the surrounding tissue or structure during a filling process, the overflowed excess should be desirably absorbed by the surrounding body tissue and cause tissue growth and recovery.
In contrast to endodontic procedures, in certain other dental procedures the pulp of the tooth is left intact. Where the pulp is exposed, a xe2x80x9cpulp cappingxe2x80x9d compound is required which will preserve the vitality of the pulp. Pulp capping compounds must also be non-toxic, and cannot result in any irritation to the pulp. Ideal pulp capping compounds also allow for regrowth of the surrounding tissue and dentine. Calcium hydroxide-based pulp capping compounds are therefore common, as described in U.S. Pat. No. 3,047,400, and in U.S. Pat. No. 4,240,832, which discloses use of condensates of alkyl salicylates with aldehydes reacted with calcium hydroxide or calcium oxide. Despite these advances in the art, there remains a need for pulp capping materials which are biocompatible, non-toxic, and which have advantageous handling properties.
The above-discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by compositions comprising degradable macromonomers having biodegradable segments selected from the group consisting of poly(lactide), poly(glycolide), and poly(caprolactone), together with terminal acrylate or methacrylate functionality, a curing composition, and optionally a co-polymerizable acrylate or methacrylate monomer. Degradable macromonomers are manufactured by the polymerization of cyclic lactide, glycolide, or caprolactone in the presence of a compound having at least one active hydrogen and at least one acrylate or methacrylate functionality. Preferred active hydrogen containing acrylate or methacrylate compounds comprise 2-hydroxyethyl methacrylate, hydroxypolyethyl methacrylate, phenoxy-2-hydroxypropyl methacrylate, and the like. Preferred co-polymerizable acrylate or methacrylate monomers include diluent monomers such as 1,6-hexanediol dimethacrylate, triethylene glycol trimethacrylate and 2-hydroxyethyl methacrylate. Degradable macromonomers can also be manufactured by the esterification of hydroxyl-group(s) terminated macromonomers of the above-mentioned hydroxy acids with acrylic acid, methacrylic acid and their derivatives. Depending on their use, the degradable macromonomer compositions further comprise one or more organic or inorganic fillers and one or more radiopacity-imparting agents. A degradable macromonomer means degradation by means of hydrolysis and/or biodegredation.
The present compositions are expected to be biocompatible and biodegradable, which advantageously allows for tissue regrowth. The degradable macromonomer compositions therefore find particular utility as root canal sealants, implant materials, and as pulp capping compositions. The above-discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description.
The present compositions comprise degradable macromonomers having terminal acrylate or methacrylate groups, a curing agent, and optionally one or more co-polymerizable acrylate or methacrylate monomer. Depending on their use, the degradable macromonomer compositions further comprise optional organic or inorganic filler and a radiopacity-imparting agent.
Degradable macromonomers having terminal acrylate or methacrylate groups are obtained by the polymerization and copolymerization of lactide, glycolide or caprolactone in the presence of a compound having at least one active hydrogen, such as an amine or a hydroxyl group, and at least one acrylate or methacrylate functionality. Such compounds include but are not limited to hydroxyalkyl acrylates and methacrylates wherein the alkyl group has from 1 to 12 carbons, such as 2-hydroxyethyl methacrylate (HEMA), 2-hydroxyethyl acrylate, diethylene glycol monomethacrylate, diethylene glycol monoacrylate, hydroxypropyl methacrylate, hydroxypropyl acrylate, tetraethyleneglycol monomethacrylate, tetraethyleneglycol monoacrylate, pentaethyleneglycol monomethacrylate, pentaethyleneglycol monoacrylate, dipropyleneglycol monomethacrylate, dipropyleneglycol monoacrylate, hydroxy polyethyl methacrylates, phenoxyhydroxyphenyl methacrylate and the like. HEMA is preferred. Degradable macromonomers having terminal acrylate or methacrylate groups can also be manufactured by the esterification of hydroxyl-group(s) terminated macromonomers of the above mentioned hydroxy acids with acrylic acid, methacrylic acid and their derivatives.
Lactide is the cyclic dimer of lactic acid, and is available as both L-lactide ((3S)-cis-3,6-dimethyl-1,4-dioxane-2,5-dione) and D,L-lactide (3,6-dimethyl-1,4-dioxane-2,5-dione). Polymerization of lactide with HEMA, for example, yields a poly(lactide-HEMA) (hereinafter PLAMA) macromonomer having the following structure (I), wherein m=1, nxe2x89xa71, and G is hydroxyl, or acrylate or methacrylate containing terminal non-polymerizable esters: 
Synthesis of suitable poly(lactic acid) macromonomers having terminal acrylate or methacrylate groups is described by S. J. Huang and J. M. Onyari, in xe2x80x9cMulticomponent Polymers of Poly(Lactic) Acid Macromonomers With Methacrylate Terminal and Copolymers of Poly(2-Hydroxyethyl Methacrylate)xe2x80x9d, in Journal of Macromolecular Sciencexe2x80x94Pure and Applied Chemistry, Volume A33, No. 5, pp. 571-584 (1996); by S. J. Huang and J. M. Onyari in Polymer Material Science and Engineering, Volume 72, No. 1, p. 137; by I. Barakat, P. Dubois, R. Jerome, P. Teyssie, and E. Goethais, in Journal of Polymer Science, Polymer Chem. Ed., Vol. 32, p. 2099 (1994); and by J. L. Eguiburu, M. J. F. Berridi, and J. San Romain, Polymer, Vol. 36, No. 1, p. 173 (1995). All of the preceding references are incorporated herein in their entirety.
Polymerization of glycolide with HEMA, for example, yields a poly(glycolide-HEMA) macromonomer having the following structure (II), wherein m=1, nxe2x89xa71, and G is hydroxyl, or acrylate or methacrylate containing terminal non-polymerizable esters: 
Polymerization of caprolactone with HEMA yields a poly(caprolactone-HEMA) macromonomer having the following structure (III), wherein m=1, nxe2x89xa71, and G is hydroxyl, or acrylate or methacrylate containing terminal non-polymerizable esters: 
Copolymerization of a mixture of lactide, glycolide, and caprolactone with HEMA yields a macromonomer having the following structure (IV), wherein m=1, n1, n2, and n3 are each independently one or greater, and G is hydroxyl, or acrylate or methacrylate containing terminal non-polymerizable esters: 
Copolymerization of a mixture of lactide and glycolide with HEMA yields PGLMA, a macromonomer having the following structure (V), wherein m=1, n1 and n2 are each independently one or greater, and G is hydroxyl, or acrylate or methacrylate containing terminal non-polymerizable esters: 
Another preferred degradable macromonomer is commercially available 2-(caprolactone)ethyl methacrylate (CLMA).
The optional co-polymerizable acrylate or methacrylate monomer is selected from those known for use as dental materials, and is typically present in amounts in the range from 0% to 95% by weight of the total composition. Multi-functional, diluent, i.e., low viscosity monomers, are preferred. Such monomers provide crosslinking and allow the viscosity of the composition to be adjusted for easy delivery to the root canal, while maintaining advantageous physical properties of the polymerized product. Exemplary diluent monomers include but are not limited to liquid dimethacrylate, trimethacrylate, or higher monomers, such as glycerol dimethacrylate, ethylene glycol dimethacrylate, tri(ethylene glycol) dimethacrylate (hereinafter TEGDMA), tetra(methylene glycol) dimethacrylate, trimethylolpropane trimethacrylate, 1,6-hexanediol dimethacrylate (hereinafter HDDMA), 2-hydroxyethyl acrylate and 1,3-butanediol dimethacrylate. These monomers are characterized by relatively low molecular weight (e.g., 400 or less) and low viscosity.
Other monomers may be used in combination with the foregoing co-polymerizable monomers, including viscous methacrylate-based monomers such as 2,2xe2x80x2-bis [4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane (hereinafter xe2x80x9cBis-GMAxe2x80x9d) as described in U.S. Pat. No. 3,066,112 to Bowen, which is incorporated by reference herein, or non-hydroxylated resins such as urethane dimethacrylate (hereinafter xe2x80x9cUDMAxe2x80x9d), or alkylated hydroxyl-containing resins such as ethoxylated bisphenol A dimethacrylate (hereinafter xe2x80x9cEBPDMAxe2x80x9d). EBPDMA in particular is effective in reducing the water sorption of the final product. A combination of the aforementioned resins may also be used.
The acrylate- or methacrylate-terminated degradable macromonomer compositions further comprise a curing composition. Suitable curing compositions for use with acrylate or methacrylate-based monomers are known in the art, and may be light cure, heat-cure, or a self cure system, or a combination thereof. Use of a dual-cure system and optional accelerators yields a composition that cures evenly and completely.
The light cure system is selected from known light-activated polymerization initiators, including but not being limited to benzil, benzoin, benzoin methyl ether, DL-camphorquinone (CQ) and benzil diketones. Either UV-activated cure or visible light-activated cure (approx. 230 to 750 nm) is acceptable. The amount of photoinitiator is selected according to the curing rate desired. A minimally catalytically effective amount is generally about 0.01% by weight of the polymeric components, and will lead to a slower cure. Faster rates of cure are achieved with amounts of catalyst in the range from greater than about 0.01% to about 5% by weight of the polymeric component.
The heat-cure initiator is selected from those known in the art such as benzoyl peroxide, lauroyl peroxide, dicumyl peroxide, 1,1xe2x80x2-azobis(cyclohexanecarbonitrile), or other free radical initiators. The amount of free-radical catalyst is selected according to the curing rate desired. A minimally catalytically effective amount is generally about 0.5% by weight of the polymeric components, and will lead to a slower cure. Faster rates of cure are achieved with amounts of catalyst in the range from above about 0.5% to about 6.0% by weight of the polymeric component. In one embodiment, the heat-cure initiator is activated by the heat of reaction generated by the light-activated polymerization process. This embodiment is particularly advantageous because the composition may be supplied to the practitioner pre-mixed, that is, as a single-component mixture ready for application to the site of restoration. In a particularly preferred embodiment, the composition is supplied in pre-packaged syringes, compules, or cartridges.
Optional cure accelerators may further be included in the light curing composition. Polymerization accelerators are the various organic tertiary amines well known in the art. In visible light compositions, the tertiary amines are generally acrylate derivatives such as 2-(diethylamino)ethyl methacrylate (commonly known as xe2x80x9cDEAEMAxe2x80x9d) and 2-(dimethylamino)ethyl methacrylate, in amounts in the range from about 0.05 to about 0.5 percent by weight of the polymeric composition.
Alternatively, the composition may be formulated with as a self-curing two-part system which is stored separately and mixed in equal amounts prior to use to initiate cure. Self-cure systems comprise an initiator such as a peroxide in one part, and an accelerator such as a tertiary amine, generally tertiary aromatic amines such as ethyl 4-(dimethylamino)benzoate (commonly known as xe2x80x9cEDMABxe2x80x9d), 2-[4-(dimethylamino)phenyl]ethanol, N,N-dimethyl-p-toluidine (DMPT), bis(hydroxyethyl)-p-toluidine, and triethanolamine in a second part. Such accelerators are generally present in the range from about 0.5 to about 4.0% by weight of the polymeric component. Another self-curing system comprises of thiourea or thiourea derivatives as the reductant and hydrogen peroxide as the oxidant, as described in U.S. Pat. No. 3,991,008. Both parts generally comprise the degradable macromonomer, co-polymerizable acrylate or methacrylate monomer, and filler in various amounts, with the initiator, for example dibenzoyl peroxide (BPO), being stored in one part, and the accelerator, e.g., N,N-dihydroxyethyl-p-toluidine being stored in another part. Equal amounts of part A and Part B are mixed by the dentist or technician immediately prior to use.
The acrylate- or methacrylate-terminated degradable macromonomer compositions further preferably comprise a filler system, wherein the filler comprises at least 5%, preferably at least 25%, and most preferably at least about 50% by weight of an inorganic calcium-containing compound, for example, calcium hydroxide, calcium phosphates, tricalcium phosphate, or calcium oxide, based on the total composition.
Other fillers which may be used in combination with the calcium-based compound include inorganic and organic particulates and fibrous fillers known in the art, such as particulate poly(lactide), poly(glycolide), poly(lactide-co-glycolide) or poly(methacrylate), or particulate or fibrous silica, silicate glass, quartz, barium silicate, strontium silicate, barium borosilicate, strontium borosilicate, borosilicate, lithium silicate, amorphous silica, ammoniated or deammoniated calcium phosphate and alumina, zirconia, tin oxide, and titania. Particularly suitable fillers are those having a particle size ranging from about 0.1-5.0 micron, with a fumed silica of 0.001 to about 0.07 microns and prepared by a series of milling steps comprising wet milling in an aqueous medium, surface etch milling and silanizing milling in a silane solution. Some of the aforementioned inorganic filling materials are disclosed in commonly-assigned U.S. Pat. Nos. 4,544,359 and 4,547,531 to Waknine, the pertinent portions of which are incorporated herein by reference.
It is also within the scope of the present invention that certain radiopaque/high refractive index materials, such as apatites, may be used as filler materials. Suitable high refractive index filler materials include, but are not limited to, high refractive index silica glass fillers, calcium silicate based fillers such as apatites, hydroxyapatites or modified hydroxyapatite compositions. Alternatively, inert, non-toxic radiopaque materials such as barium sulfate and bismuth subcarbonate may be included.
The compositions may further comprise anti-oxidants, for example BHT (2,6-di-tert-butyl-4-methylphenol) or hydroquinone methyl ether in amounts in the range from about 0.1 to about 0.3% by weight of the polymerizable components; ultraviolet stabilizers to prevent discoloration, for example benzophenones such as 2-hydroxy-4-methoxybenzophenone, benzotriazoles, such as 2-(2xe2x80x2-hydroxy-5xe2x80x2-methylphenyl)benzotriazole, 2-(2-hydroxy-5-tert-octylphenyl)benzotriazole (available under the trade name UV-54 from American Cyanamid Company) and other derivatives thereof; fluorescent whitening agents such as 2,5-bis(5-tert-butyl-2-benzoxazole) thiophene (available under the trade name UV-OB); trace amounts of FDA and FDC approved dyes, for example carbon black, yellow No. 5, yellow No. 6, and the like; and other additives known in the art.
Medicaments may also be included in the compositions in an amount effective to prevent infection and/or inflammation, generally from about 1% to about 10% by weight of the total composition. Suitable medicaments include but are not limited to pain relieving agents such as Novocaine (procaine hydrochloride), Benzocain (ethyl aminobenzoate), ascorbic acid, butacaine sulfonate, dibutacaine hydrochloride, anti-biotics such as sulfadiazine, procaine penicillin, aureomycin, streptomycin, terramycin, chloramphenicol, butabarbital, diethyl stilbestrol, and anti-inflammation agents such as p-aminosalicylic acid, aspirin, and the like.
Another preferred embodiment of the present invention is a method of forming a dental restorative comprising preparing a site to be restored in a tooth; and applying a composition comprising (a) at least one degradable macromonomer having terminal acrylate or methacrylate groups; (b) a curing composition; and (c) optionally one or more co-polymerizable acrylate or methacrylate monomers.
The present invention is preferable to the currently available art for root canal sealants, implant materials, and pulp capping compositions because the compositions of the present invention are expected to be non-toxic, biodegradable and biocompatible. These properties are ideal for tissue regrowth in the surrounding tissue and dentine when the compositions are used in pulp capping procedures or root canal procedures. Also, the present compositions have low shrinkage, which is required for use as root canal sealants.
The invention is further illustrated by the following non-limiting Examples. Synthesis of PLAMA was in accordance with Huang (1996).